The flow cytometry results showed that SAHA had a higher affinity for GC cells than for normal gastric cells. SAHA can be enriched in GC tissues. However, there was also a high-concentration distribution in normal organs such as the stomach and lungs, suggesting potential side effects. In addition, we found that among the HDAC family members, HDAC9 was the most significantly upregulated in GC cells, and we verified this upregulation in GC tissues. Further experiments confirmed that knockdown of HDAC9 inhibits cell growth, reduces colony formation, and induces apoptosis and cell cycle arrest. These results suggest that HDAC9 has an oncogenic role in GC. Moreover, HDAC9 siRNA suppressed GC tumor growth and enhanced the antitumor efficacy of cisplatin in GC treatment by inhibiting the proliferation and inducing the apoptosis of GC cells in vitro and in vivo. Our findings suggest that the development of HDAC9-selective HDACis is a potential approach to improve the efficacy of chemotherapy and reduce systemic toxicity. test. Statistical significance was inferred for P?Epoxomicin in a separate window Fig. 1 The effect of SAHA on the proliferation of gastric cancer cells.a A real-time cell proliferation assay using the xCELLigence system showed that SAHA treatment induced the death of BGC-823 cells in both a concentration- and time-dependent manner. b Determination of the IC50 of SAHA in BGC-823 and SGC-7901 GC cells treated with SAHA for 72?h Binding affinity of SAHA for GC cells The binding capacity and affinity of FITC-labeled SAHA for GC cells was assessed by flow cytometry. The flow cytometry data showed that the percentage and fluorescence intensity of positive cells in the P2 gate steadily increased with increasing concentrations of FITC-SAHA, wheresas there was a negligible change Epoxomicin in the percentage with increasing concentrations of free FITC (Fig. Epoxomicin 2aCc). The mean percentages of positive cells incubated with 1?m FITC-SAHA or free FITC were 66.9% and 1.2%, respectively, in BGC-823 cells and 28.8% and 1.7%, respectively, in Epoxomicin MKN-45 cells (Fig. 2e, f). In addition, we observed a stronger affinity of the SAHA probe for GC cells than for normal gastric mucosal cells (GES-1). The mean percentage of positive GES-1 cells was only 3.2% when treated with 1?m FITC-SAHA. This percentage was significantly less than that of BGC-823 and MKN-45 cells (Fig. 2dCf). Fluorescence imaging of GC cells with FITC-SAHA also showed that SAHA was mainly enriched in cell nuclei and that the fluorescence signal was distinctly brighter in GC cells than in GES-1 cells (Supplementary Fig. 1). These results demonstrated higher binding specificity and affinity of SAHA for GC cells than for normal gastric cells. Open in a separate window Fig. 2 Binding capacity and affinity of SAHA for GC cells.aCc The GES-1, BGC-823, and MKN-45 cell lines were incubated with various concentrations of FITC-SAHA for 4?h. Fluorescence was analyzed by flow cytometry. GES-1, BGC-823, and MKN-45 cells treated with various concentrations of free FITC were used as controls. dCf The proportion of positive cells labeled by FITC-SAHA or free FITC was calculated. All experiments were repeated three times In vivo near-infrared fluorescence imaging of IRDye800CW-SAHA in GC xenograft mouse models To examine the specificity of SAHA for recognizing GC cells in vivo, an IRDye800CW-labeled SAHA probe was intravenously injected into PPARG BGC-823 and SGC-7901 tumor-bearing mice, and the FMI was dynamically monitored using a small animal imaging system. Specific and increased fluorescence signals in tumors were observable 8?h after injection of the imaging probe.